Screw-cutting lathe



Oct. 23, 1951 E. RITTER 2,572,759

SCREW-CUTTING LATHE Filed Sept. 3, 1948 4 Sheets-Sheet 3 r0 4, 1 5 05 w 6 x 6 a I n 7 a: i mum 2 77 0 m a 1 3 w aha. 7. 2 M 4 2 9x 5 \4 7 3 7 2 7 W 8 5 6 7 9 9 8 4 G 4 2 6 0 g 4 9. 7 w 7 o 0 4 3 4 0 6 5 3 4 3 3 z 4 l 4. 3 m 3 4 W 3 M k 4 I 6 2/ a M 2 MI W. 5 z a? Patented Oct. 23, 1 951 UNITED- STAT ES arsur" OFFICE;

SCREW- CUTTING LATHE Eugene L. Bitter, Cincinnati, Ohio, assignor to The Cincinnati Lathe & ToolCo'.,' Cincinnati, Ohio, a corporation of Ohio Application September 3, 1943, Serial No, 47,667

6 Claims.

This invention-relates. to machine tools and more particularly to improvements in screw cutting lathes.

' One ofthe objects of this invention is to pro vide. an improved screw cutting lathe which may Another object'of this'invention is to provide an improved gearbox mechanism which when utilized with a millimeter pitch" lead screw may be-readi1y arranged forcutting either millimeter pitch threads -or-American standard threads.

Stillanother object of this invention is to provide agear box which maybe adjusted to yield found-ifirent series of ratios or speeds between awork-spindle and lead screw'of a screw-cuttinglathe-so that either an American-standard thread ora millimeter pitch thread may be cut' regardless of whether the lead screw has an American standard thread or a millimeter pitch thread.

Other-,objects and advantages of the present inventionshould be readily apparent b-y-reference to thefollowing specification, considered in conjunctionwith the accompanying drawings-forming'a part thereofland itis to'be understood that any modifications may be made: in .the exact structural. details thereshown and: described,

within. the scope of the :appendedclaims, without departing from or exceeding the spirit of the.

invention.

Referring to -the drawings in which like reference numerals indicate like or similar parts:

Figure l is an end elevation of the-headstock of a screw-cutting lathe showing the change gear drive fromthe spindle.

Figure 2 is a section on theline 2-2 of Figure 1 Figure 3 isa-front elevation of the headstock end of a lathe showing the-mechanism of this invention applied thereto.

Figure 4 is a View similar toFigure .2 with the partsarranged for cutting metric'screwswith an American standard lead screw.

Figure 5 isa detailsection on the-line-5-5 of Figure-3.

Figure 6 is a detail section on the 1ine 6 6 of Figure .3.

Figure '7 is a viewsiniilar to Figure 2 withth'e parts arranged for cutting metric screws with ametric lead screw;

Figure 8 is a detail section on the line 8 -8 of Figure 3.

Figure 9, is detailsection on the'lin'e 5+9 of Figure 31' Figure'lo'is a. section similar to Figure 2 with the parts arranged for cutting American standard screwswith a metric lead screw. I This invention relates to screw and more" particularly to improvingthe'con structicn of such machines for the purpose of making it possible to' out either American'stand ard or millimeter pitch threads 'with'the same machine; It 'is obvious that abasic machine could be provided for one of these purposes havingasuitable gear 'OOX' and a lead screvrwith an Amer ican standard thread for cutting American stand ard threads; and for the other purpose, a differ ent gear boX-with'a lead-screw having a-millimeter" pitch" thread for cutting metric threads:

In screw cutting machines the lead screw-is driven from the work spindle through' 'a trans mission which may be adjusted to cause rotation of the lead screw in some predetermined"ratioto one rotation ofthe spindle in-accordance with" he pitch of the'thread desired to becut. accordance with this invention, a'common transmission is provided; comprising a'change gear mechanisnrand agear box of such a nature that Y a single machine may bebuilt which is soadjustable that the spindlemay beconnected in properdriving -ratioswith either an American standardlead'screw or a millimeter pitch lead screw for cutting-either type of thread with either type of lead'screw. Thus; by the-use of a single transmission-mechanism such as disclosed by this in vention, a'basic machine havingan American standard lead'screw or abasic machine 'havinga metric standard leadscrew maybeprovided; buteach basic machine has the capacity 'f or being readjusted for cutting the other type 'ofthrea Referring nowto the drawings, and more particularly to Figures "1 and 2, there is shownin Figure 1 one arrangement'ota change gear mechanism; and contained in the gear 'box l0;-

shown in Figure 2, is a variable speed transmissionwhich connectsthe change gear mechanis'in' to the lead screw; said-"transmission being shown in theproperadjusted relation for cutting Amer ican standard threads witha lead screwhav'in'g an Americanstandard thread.

InFigure 1, the reference numeral ll indicates the bed 'of' a screw cutting lathe having the gear boxlfi attached to the front side, and uponjth'e" top of the bed is a spindle housing IZ'haVinga work spindle as suitably journaled therein." This spindleis driven from any suitable source'votcutting lathes 3 power not shown and is utilized herein as the driver for the transmission mechanism which couples the spindle l3 to an American standard lead screw indicated by the reference numeral M in Figure 2. The gear box has a drive shaft |5 which serves as a power input shaft, and this shaft is connected to the spindle |3 by a change gear mechanism which in this embodiment comprises the gears |6, l1, and I8.

The gear H3 is secured to the end of the spindle l3 while intermediate gear- H is journaled for free rotation on a stud l8 which is carried by an adjustable arm I9 that is pivotally mounted on the fixed sleeve 20 which is concentric to the axis of the shaft l5. The gear I8 is keyed to the shaft i5, and the arm I9 is angularly adjusted to place the idler gear |1 into mesh with the gears I6 and I8 and is then clamped in position by the clamping nuts 2| which are threaded on the ends of stud screws 22 which pass through elongated slots 23 formed in the arm l9.

In the gear box l0, there is a shiftable gear couplet 23' which is splined on the shaft l5 for selective engagement of gear 24 with gear 25, or alternatively gear 26 with gear 21. The gears 25 and 21 are integral, thus forming a couplet 28 which is keyed to the shaft 29. Thus, the shaft 29 may be driven at two different rates from theshaft |5 in accordance with the positioning of the couplet 23. The shaft 29 is provided with a long spline 30 to which is keyed a gear 3| which is mounted in an oscillatably and axially shiftable shifter 32. The shifter 32 is adapted to oscillate about the axis of the shaft 29 for the purpose of engaging a tumbler gear 33 journaled therein with any one of a set of stepped cone gears carried by an intermediate shaft 34. There are eight gears shown in the set indicated by the reference numerals 43, 35, 36, 31, 38, 39, 40,.and 4|, although this number may be varied. These cone gears are keyed to the shaft 34 so that rotation of any one of these gears by the shaft 29 through the gears 3| and 33 will cause rotation of all of these gears.

The shaft 34 carries an additional gear 42 which is constantly in mesh with a gear 46 which is supported for free rotation on a back gear shaft 45 journaled at opposite ends in the gear box ID. The gear 43 is in constant mesh with gear 44 which is also supported for free rotation on the shaft 45. A third gear 41, slidably splined on the shaft 45 intermediate the gears 44 and 46, is provided with clutch teeth on opposite faces for engagement with clutch teeth on the adjacent faces of gears 44 and 46. When the gear 41 is in the position shown in Figure 2 it is in mesh with the gear 38, but when it is shifted to the left, as viewed in this figure, it becomes disengaged from the gear 38 but clutched to the gear 44 and thus serves to connect the gear 44 for rotation with the shaft 45. When the gear 41 is shifted to the right, it clutches gear 46 in driving relation to the shaft 45. Thus, the gear 41 is capable of connecting the shaft 34 in three different driving ratios to the shaft 45 and regardless of which one of the cone gears is being driven. It will thus be seen that by means of the two selections that may be made by the shiftable couplet 23, and the eight different connections that can be made between the shaft 29 and 34 and the three different connections that can be made between the shaft 34 and the shaft 45 that a total of 48 different speeds can be obtained for the rotation of shaft 45, and this means 48 different ratios between the rate of rotation of the work and the rate of travel of the threading tool.

The shaft 45 is adapted to be reversibly connected to the lead screw M in a one to one ratio by means of a shiftable reversing clutch 48 which has clutch teeth on opposite faces for engaging similarly formed clutch teeth on the adjacent faces of gears 49 and 50 which are supported for free rotation on the shaft 5| which forms an extension of the lead screw l4. The gear 49 is intermeshed with the gear 52 of the couplet 53 which is supported directly on the shaft 45, while the gear 50 is connected by an intermediate idler 54 to the gear 55 of the couplet 53 whereby the gears 49 and so will be driven in opposite directions. Attention is invited to the fact that the gear couplet 53 has clutch teeth 56 on the end face thereof for engagement with a removable sleeve 51, which sleeve is keyed at 58 to the shaft 45 and thus serves as a driving connection between the shaft 45 and the couplet 53. This sleeve is journaled in a thimble 59 which is threaded at 66 into the end wall of the gear box. This thimble is interchangeable with a second thimble 6| located in the lower part of the box for supporting the end of the shaft 29.

The thimble 6| is threaded at 62 in the end wall of the gear box, and the thread is the same size and the number of threads as on the end of thimble 59 whereby the thimble may be interchanged as explained hereafter.

It will be noted that the thimble 6| has a smaller bore 63 in which the end of the shaft 29 is journaled, and a larger bore 64 which forms a clearance for the key 65 permanently fixed in the shaft 29 whereby the shaft is free to rotate independent of the thimble 6|.

The purpose of the interchangeable thimbles is that in some cases, as in that shown in Figure 2, it is desirable that the gear 53 be connected to the shaft 45, while in other cases it is desirable that the gear 53 be supported for free rotation on the shaft 45 and that the gear 54 be connected in driving relation to the shaft 29. By simply interchanging the thimbles 59 and 6| it is possible to make these changes in driving'relationship of the gears with respect to their supporting shafts.

In the form of the invention shown in Figure 2, the lead screw I4 is assumed to have an American standard thread cut thereon and the gearing of the transmission mechanism is arranged so that shifting of the various gear elements of the gear box makes possible a selective. range of threads which will be in accordance with the American standard system. For example, by making the change gear mechanism between the shaft l3 and the shaft |5 in the ratio of three to four; the shiftable gear couplet 23' in the ratio of one to three between gear 24 and gear 25; and eight to three between the gear 26 and 21; the cone gears in eight ratios with respect to the tumbler gear ranging from one to one when intermeshed with gear 43, to twelve to twenty-three when intermeshed with gear 42; and the back gears in the ratio of two to one between gears 42 and 46, one to one between gears 38 and 41, and one to two between gears 43 and 44, a range of 48 different feeds and threads may be cut. One limit of this range or the greatest number of threads per inch would be computed by taking the lowest ratio of each shiftable unit and therefore would be equal to 3/4 X 1/3 X 12/23 X 1/2 equal to 3/46. It will now be obvious that with a p. 6 pitch lead screw that this would yield 92 threads. 7

amazed 5 p'r incht 'It isobvious that this limitncouldzbe changed by using a 'diff'rent'slpitchedfleact screw; 'Taking "th'e high'estratios itwoul'd-z' give 374' 8/3 1" 2 "eq1ial -4; and thi'sz' with a 6 pitch =lead screw would give 1 /g -threadsiper inch:v Referring :now" to Figure 6;? therer-is shownztheg mechanism for shif ting the "gear *couplet 2 35 com-:--

prising a' shifter member 6 5 having a'uportioh 161-- which interfits==th shifter groove 'fi8 f'forme'da inz.

the member 23 the memberfifilbeing.ikeyedvto rotatable shat-UB9. This -:'shaft"'-is supportedat opposite ends for'rotati'on in the walls. of -:the gear; 1 box U and is provided with 'an op'eratlng. handles I which" carries a spri'ng 'press'ed detent: ball i-H which is ad a'pted to alternatively engagei detent 12. or"'|3"'tormed in the frontiwall" 14 m 'thexgearjb'ox lfl' as-shown in Figure3. Thus, the-shaft 29smay;

be-drivenin'two idifierent' rati'os by the shaft: l: 1

In Figure *5 is shown the: mechanism: "for fsh'iftin'g the tumbler gear 33 comprisin'gt the. "shifter member' 3 2 which" is oscillatably :supported...onith'e shaft" 29 "as previously described; and this shifter;

member p'asses:through' a slot 15 formed ina thei' Wall offthe gear box and has? attached; to) its' end-on the outside of the -box' a plate :TBJWhiclrha-s an integrally' formed handle"11. The. p'lat'ei'srof;

sumcient' size to close the opening and on. its upper "surface is provided witha series or ino'tohes I8 corresponding {in nlinibe o :the :numberof cone gears: These notches' -are adapted? to rem? brace'a locating pint-19' secured in theu-wall l 0 .of

the' gear=box.-

Ii-knob 8| is secured to the-end of-a retractable pin 81' which is slidablymountediin the handle?! 7 and "normally urged byfa 'sp'ring'v82 iitOn. hold the end 'of- 'the pin -83 :inengalgement' with 'onerof :a series of holes 84 drilled in the wall of the gear box. Thus by'retractin'g the pin'8l the; shifter 32 "maybe rotated-about the shaft 29 to lift the gear=33 out of engagement with one cone'gear,

then shifted axially with respect to the shaft 29 to position the gear 33in alignment with another-- conegear-Z for? 'intermeshing therewith upon subsequent rotation of the shifter '32 in the opposite direction. Thus, by means of this mechanism the ge'ar 33 rnay be selectively ,intermeshed'and locked in drivin'g relation with any one of the various cone gears.

InfFigure8-isshownthe mechanism for shift-v ingith'e'. back gearr ll with respect to itsshaft 45 comprisinga 'shifterfork' 85 which-is pivotally connectedto'the'shifter. arm -86-secured to one end of' arshaft 81 which extends'through the wall-of theigear box ID for attachment of an-operating handle 88 thereto. The -'operating.handle -88 has a springpressed' detent ball 89 mounted therein for selective engagement with one of three detents 9fl 'formed inan angleplate-9l secured to the end The mechanism for shifting of the 'gear. box. the-reversing clutch 48-is shown in Figure 9 and comprises-a shifter arm-92 whichhasashifter fork.93 supported in the end thereof andiin engagement with the shifter groove 94 formed in thnclutchll8t The-arm 92 is-securedto theend When itis desired to cutmetric threads with an'Americanstandard pitch lead screwsuch as that described in -co'nnection-"with Figure -2, the=' endwalr 99*of "the gearbox- I 0; asshowrr in'Fi'gure ear-ratios remain=thesame Lids removed and 'thetransposable=-geanhoublet 28 is removed from its:-dottedfline -po'sitionon shaft 29 and mounted on the keyed endofshaft whereby theshaft' i S t/ill now+drive=theshaft 45 rather than' tlie shaffi n. 4 additiom thei thimbles 6| and '59' are interehanged whereby-the drivenew I passes from the shaft d5 -througtr the back gears to" the conegears,' from the cone ge'a through": the tumbler: gear to the shaft 2 9 -2111 sleeve '51 keyed to'the end thereof te -the gear clutched with the sleeve il;- Thegearfi drivesi gear L4 9 :through .the gear "couple't" 53 which 'wi-lh rotate independently of the shaft gaud also drives: gear b'ut inthe opposite directiona In additio'mthechange gees-1s is removed from theshaft I 5 and -"a substitutrgear [06* isr s mountedzin its steadzw The idler gear l1-"shown-:1 f' Fl ureez is'1 reversed'in positionand conversion gear -ln'liis compounded with' th g l'lzby being mounted'ozr the keyed 'h'ub 1 02 gear l 1 and in' position to mesh with the-gear and-thus be driven-:th'ereby while-the gear 1 i, is in position to mesh with the gearl 003 r f The conversion gear is. preferably'providdwith 127 teeth which is a-multiple-of-25.-4,theresb'eings 25.4 'millimeters in' an -inch. -Thus: the' -overa'l ratio .of:tthe :change -"gear's-becomes 13572545-A-1 thoughsthegear -couplet 28 has= been shifted o the shaft 545, the high and "-low ratios between? shaft I5 and shaft 45 still remains 8 to 3}and'bne to three. Since the direction-of-drive through the cone gears =isnowirian =opposite-direction, the :range of .lratios through thes g jsjfnowy from one to one, 1 to two --to' "one; While the back-i pitch o1 one- 'thread: in millimeters would? be?" Edualto '12t5.4/6- -and' -'therefore"if" the" fihaIira 104s mu ipli'e'd by thisfi'gure-We'woul a. 2.-25/25'.4 -25;4/6 equal'1375mm. The othgfi ihiii would -"-beequal toBE/254x8/3X'2/1X23yl2' equals 45 x 16/127 Multiplyingfithis' by the pitch? of the 'sixthread'sperinch ladscYew 111mm limeterwe-would have4-5 -16 12 1 2 5".4/6 was to 23 mm. Thus, by simply "shiftinglfthef gearf" couplet- 28 and--reversing-"the thi'mbles 59"and B1 1 and adding the metric" conversion Lgeiarxin' the change gear -mechanism;'-;metric'-threads ma yjibe cut-with an American lead 'screw having a mil'- limeter pitch'rangingfromfi375 to'"23. is W In the arrangement shownin Figure, 7 it is as; sumedthat' th'elead screw Mfhas'a metricttliread' of 4 *mm." pitch 7 and thetra'nsmission a range..- rnent issuch that metric. pitch screws mayibefcut. 1; 1n awork piece. It.,wil1. be noticed that the transmission the gear box remains the same.v as that shownin Figure-.4r while the .changeggeaialmechanism .has only-been changed by; -trem'bv1n the metriccon-version gear qllll and directlyicoug pllng theidler .gear -I 1 between =1the..gears.:l 6 I00 whereby: the; gear: H. becomestsimplyian idler: gear. 1 By: making. the change gear ratio:-9; 16=and; with. the ratios in the-gear box remaini-ngthe same, one-limit of-the range of threadsthatcan be cut would be:9/16 '1/3 1 1/2 equals 3/32; and this multiplied by--'the pitch ofth'e 'le'ad screw; whichis 4 mm;, would give 3/8 or 1375 him? pitch of thread. The other limit would-b fd d r-.-

asfol1ows:- 9/16X8/3x2x23/12 equals" 69/12 times the pitch of thelead screw' in millimeters wouldequal 23- mm$ Thus; a range "of threads metric from .375 mm, to 2 3 mm. could, be cutwith the arrangement shown in Figure 7.

In Figure the transmission is shown rearranged for cutting H American standard threads for the 4 mm. pitch lead screw shown in Fi ure 7. In this figure the gear box is rearranged the same as that shown in Figure 2 and the change gear in the gearbox are the same as in Figure 2, one

limit I would be 127/160x X 12/23 x equals 127/ 160x2/23, and this multiplied by the pitch of the lead screw in inches, which would be 4/2511, would equal 1/92 or 92 threads per inch. The

other limit would be 127 160 x 8/3 x 1 x 2v equals 127/30x4/25A equals 2/3 or 1 threads per inch for the other limit.

, There has thus been provided an improved transmission mechanism for a screw cutting lathe which may be utilized with a lead screw having a thread of either pitch, that is, American standard or millimeten and which is capable of cutting either type of thread with either pitch of lead screw.

What is claimed is:

1. In a screw cutting lathe having a spindle, a variable speed mechanism including first and second shafts, and means for interconnecting said shafts in a plurality of different ratios, the combination 'of means for selectively connecting the spindle to either of said shafts whereby one of said shafts becomes the driving shaft and the other the driven shaft including av power input shaft having a permanent gear couple thereon, a transposable gear couple connectible to either the first or the second shaft, means to shift said first-named gear couple alternately into engagement with eithergear of said transposable gear couple, change gears including an idler gear cou- ,4

transposable gear is mounted on the back gear shaft.

2. In a screw cutting lathe havinga spindle, a variable speed mechanism includingfirst and second shafts, and means for interconnecting said 1 first or the second shaft, means to shift said firstnamed gear couple alternately into engagement with either gear of said transposable gear couple, change gears including an idler gear coupling the spindle to said power shaft in a prescribed ratio for each position of said transposable gear, a

translating gear compoundable with the idler gear in a position to be driven therefrom when a the transposable gear is mounted on the first shaft, and in a second position for transmitting v power to. the idler gear when the transposable gear is mounted on the back gear shaft, a feed screw journaled in the lathe having a pair'of reverse gears loosely mounted thereon and an interposed reversing clutch, idler gears mounted on said first and second shafts respectively and operatively connected to said reverse gears, and means to connect the first shaft or the second shaft whichever is being driven by the other to its respective idler gears selectively to effect actuation of the reversing mechanism.

3. In a screw cutting lathe having a spindle, a variable speed transmission mechanism including a first shaft, a back gear shaft, an intermediate shaft having a set of cone gears thereon, and means for connecting said gears to said first and back gear shafts respectively in a pluralit of different ratios, the combination therewith of means for selectively connecting the spindle to the first shaft or back gear shaft whereby one of said shafts becomes the driving shaft and the other the driven shaft, including a power input shaft having a permanent gear thereon, a transposable gear meshing therewith for connecting either the first shaft or the back gear shaft to the input shaft, change gears on the spindle and input shaft for coupling the spindle to said input shaft in two prescribed ratios, one for each posi- V tion of the transposable gear, a pair of compound gears including a translating gear, and supporting means for reversibly positioning said compound gears between said change gears to effect alternative meshing of the translating gear with the change gear on the spindle when the transposable gear is mounted on said back gear shaft, or with the change gear on the input shaft when the transposable gear is mounted on said first shaft.

4. ma screw cutting lathe having a spindle, a variable speed transmission mechanism including a first shaft, a back gear shaft, an intermediate shaft having a set of cone gears thereon, and

means for connecting said gears to said first and back gear shafts respectively in a plurality of different ratios, the combination therewith of means for selectively connecting the spindle to the first shaft or back gear shaft whereby one of said shafts becomes the driving shaft and the,

other the driven shaft, including a power input shaft having a permanent gear thereon, a transposable gear meshing therewith for connecting either the first shaft or the back gear shaft to the input shaft, change gears on the spindle and input shaft for coupling the spindle to said input shaft in two prescribed ratios, one for each position of the transposable gear, a pair of compound gears including a translating gear, .supporting means for reversibly positioning said compound gears between said. change gears to effect alternative meshing of the translating gear with the change gear on the spindle when the transposable gear is mounted on said back gear shaft, or with the change gear on the input shaft when the transposable gear is mounted on said first shaft, and a reversing mechanism for actuation by said transmission including means for selectively connecting said mechanism for actuation selectively by the first shaft or back gear shaft whichever is being driven by the other in accordance with the position of the transposable gear.

5. In a screwcutting lathe having a spindle, a variable speed transmission mechanism including a first shaft, a back gear shaft, an intermediate shaft having a set of cone gears thereon, and;

means for connecting said gears to said firstv and back gearshafts respectively in a plurality of different ratios, the combination therewith of means for selectively connecting the spindle to the first shaft or back gear shaft whereby one of said shafts becomes the driving shaft and the other the driven shaft, including a power input shaft having a sliding gear couple splined thereon, a transposable gear couple selectively meshing therewith for connecting the input shaft to either the first shaft or the back gear shaft, change gearing coupling the spindle to said input shaft in two different ratios, one for each position of the transposable gear, including a change gear on the spindle and a change gear on said input shaft, a pair of compound gears including a translating gear, and supporting means for reversibly positioning said compound gears between said change gears to effect alternative meshing of the translating gear with the change gear on the spindle when the transposable gear is mounted on said back gear shaft, or with the change gear on the input shaft when the transposable gear is mounted on said first shaft.

6. In a screw cutting lathe having a spindle, a variable speed transmission mechanism including a first shaft, a back gear shaft, an intermediate shaft having a set of cone gears thereon, and means for connecting said gears to said first and back gear shafts respectively in a plurality of different ratios, the combination therewith of means for selectively connecting the spindle to the first shaft o back gear shaft whereby one of said shafts becomes the driving shaft and the other the driven shaft, including a power input shaft having a sliding gear couple spl ned the eon, a tr posable gear c p e electively meshing therewith for connecting the input shaft to either the first shaft or the back gear shaft, change gearing coupling the spindle to said input shaft in two different ratios, one for each position of the transposable gear, including a change gear on the spindle and a change gear on said input shaft, a pair of compound gears including a translating gear, supporting means for reversibly positioning said compound gears between said change gears to effect alternative meshing of the translating gear with the change gear on the spindle when the transposable gear is mounted on said back gear shaft, or with the change gear on the input shaft when the transposable gear is mounted on said first shaft, and a reversing mechanism for actuation by said transmission including means for connecting said mechanism for actuation selectively by the first shaft or back gear shaft whichever is being driven by the other in accordance with the position of the transposable gear.

EUGENE L. BITTER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 918,773 Schotz Apr. 20, 1909 1,074,819 Schellenbach Oct. 7, 1913 1,545,052 Ingham July 7, 1925 1,628,598 Bird May 10, 1927 1,982,613 Hgelscher Nov. 27, 1934 

